Homogeneous polyethylenes are elastomeric copolymers used in such applications as hose and tubing, wire and cable, gaskets, and single ply roofing. They are usually formulated with fillers, oils, processing aids, and stabilizing agents. The homogeneous polyethylenes generally have a polydispersity (Mw/Mn) in the range of about 2 to about 3.5, and an essentially uniform comonomer distribution.
One of the catalyst systems selected to produce polyethylene in the gas phase on a commercial scale is described in U.S. Pat. No. 4,508,842. Typically, the catalyst system is comprised of a catalyst precursor, which is the reaction product of vanadium trichloride and an electron donor, the precursor being reacted with an aluminum containing modifier, and impregnated into a silica support; a promoter such as chloroform; and a triisobutylaluminum cocatalyst. This catalyst system produces a compositionally heterogeneous resin. It does achieve good particle morphology, but the non-uniform composition and broad molecular weight distribution results in polyethylene products with poor transparency and poor heat-sealing properties.
In U.S. patent application Ser. No. 08/083,664 filed on June 28, 1993 by Bai et al, a process is provided for the production of homogeneous polyethylenes, which are relatively free of these deficiencies. While this process is certainly advantageous, industry is desirous of producing homogeneous polyethylenes having superior strain hardening properties, which are so important, for example, in blown film tubular extrusion and other film blowing processes.